Cellular data networks provide data connectivity to mobile devices having cellular network interfaces. The network is formed of a network core for handling control plane functions and data packet routing, and a radio access network (RAN) of macrocell base stations located throughout the coverage area of the mobile network for wireless communication with subscriber mobile devices. An example of a cellular network architecture is Long Term Evolution (LTE). Unlike previous generation second generation (2G) and third generation (3G) cellular networks which offer packet switched data services on top of a circuit switched voice platform, LTE is an all-packet switched data network architecture that does not support the traditional voice calling platform.
Wireless local area networks (WLANs) operating in accordance with the IEEE 802.11 family of standards (commonly referred to as Wi-Fi) are common in many user locations and provide data connectivity over a short geographic range. Typically the wireless local area network is generated and maintained by a wireless access point which acts as a packet routing interface between devices connected to the WLAN (e.g. smartphones, tablets) and local devices connected via a wired interface (televisions, network attached storage). The wireless access point serves local devices and will typically be co-located, or integrated with an external network interface such as a modem for providing a backhaul link to external networks such as the Internet via an Internet Service Provider's core network. Example backhaul technologies include Digital Subscriber Line (xDSL) copper/fiber and cable based on the Data over Cable Service Interface Specifications (DOCSIS) architecture.
Such a combined WLAN, routing and modem device will be referred to as a hub throughout the description.
Both LTE and WLANs are examples of packet switched data networks in which application data is split into packets and the packets can take any path within the network to arrive at the receiver. In contrast the circuit switched networks require a dedicated data path to be established prior to sending data along the dedicated circuit.
VoIP/VoLTE/VoWiFi
Voice over Internet Protocol (VoIP) applications are known for allowing voice communication via a packet switched network. The voice data is sampled into packets of voice data and the packets are sent over the data network.
VoIP applications are Over-The Top (OTT) services which typically require a user to generate a username identity and generally a VoIP call can only be established between two users having the same VoIP application on their mobile devices. Even where the VoIP application allows calls to conventional telephones and the caller information display shows the caller's telephone number, when the callee tries to return the call, the call is forwarded to the user's mobile, hence the call is received via the standard dialer and not the VoIP application.
Furthermore, in the VoIP service it is not possible to maintain a call if the mobile device moves out of range of the current access point and requires a handover from one access technology to another.
Voice over LTE (VoLTE) is a voice service running over LTE which uses optimized headers and priority marking to provide a voice service using the packet switched network with an aim to reducing/replacing the reliance on Circuit Switched Fall Back (CSFB) and VoIP services. This will reduce operating overheads and may allow parts of the legacy 2G and 3G platforms to be switched off.
Due to the prevalence of WLANs in many areas, the Voice over Wi-Fi (VoWiFi) or Wi-Fi Calling service has also been deployed by several network operators. In VoWiFi, the WLAN is regarded as a non-3rd Generation Partnership Project (non-3GPP) access network base station to the LTE network so that voice calls are made and received using the standard telephony software and packet data is tunneled to and from the cellular network core. VoWiFi therefore appear to extend the cellular network coverage to indoor locations where the cellular reception may be reduced. When the mobile device leaves the range of the WLAN and VoLTE is available, then at present the mobile device will register to a normal VoLTE service. It is expected that future implementations of VoWiFi will allow handovers from VoWiFi to VoLTE and VoLTE to VoWiFi.
Mobile devices such as smartphones will therefore have both a cellular network interface and a WLAN interface for data connectivity. Generally, the mobile device is configured to prefer the WLAN interface for all data connectivity when both WLAN and cellular access is available.
The Applicant's co-pending European applications EP15187793.3 and EP15203278.5 provide methods for determining when a link between the hub and the VoWiFi service is disrupted or not available and instructing the mobile device to disconnect from VoWiFi. In this way the mobile device is forced to connect to VoLTE to maintain its connection to a Multimedia Telephony service (MMTel) voice service even if the mobile device's view is that the WLAN signal quality appears to be sufficient to support VoWiFi.
In those co-pending applications, the processing is based on monitoring the link to the VoWiFi service on behalf of the mobile devices so that the presence of a stable WLAN link is not the sole determinant in whether a mobile device should use VoWiFi or VoLTE.
However, the determination to switch away from VoWiFi does not consider any circumstances of the mobile device relative to the LTE link quality.